A major operation in mineral processing involves the separation of desirable minerals from ore bodies within which the minerals are contained. Froth flotation is a common technique employed to facilitate such separation. In froth flotation, ground ore is typically fed as an aqueous slurry to froth flotation cells. The chemistry of the slurry is adjusted such that certain minerals selectively attach to air bubbles which rise upward through the slurry and are collected in froth near the top of a flotation cell. Thereafter, minerals in the froth can be separated from different minerals in the cell.
The surfaces of specific mineral particles in aqueous suspension are treated with chemicals called flotation reagents or collectors. Flotation reagents provide the desired mineral to be floated with a water-repellent air-avid coating that will easily adhere to an air bubble, which will raise the mineral through the slurry to the surface.
The valuable mineral separated and collected during the froth flotation process may be either the froth product or the underflow product. Froth is generated by vigorous agitation and aeration of the slurry in the presence of a frothing agent.
Other chemical agents can be added to the slurry to aid in separation, such as depressants or modifiers. The presence of depressants in a float generally assists in selectivity and/or stops unwanted minerals from floating. Modifiers facilitate collection of desired minerals. Modifiers include several classes of chemicals such as activators, alkalinity regulators, and dispersants. Activators are used to make a mineral surface amenable to collector coatings. Alkalinity regulators are used to control and adjust pH, an important factor in many flotation separations. Dispersants are important for control of slimes which sometimes interfere with selectivity and increase reagent consumption.
One difficulty encountered in froth flotation is the separation of chalcopyrite from a concentrate comprised of chalcopyrite and copper rimmed iron sulfide, typically pyrite. As used herein, the terms "copper rimmed" and "rimmed" refer to a copper sulfide coating which forms on at least part of the surface of iron sulfide, and in particular, pyrite. This coating forms in geological formations when, over a long period of time, chalcocite and covellite replace pyrite on the surface of the mineral.
Typically a chalcopyrite/pyrite slurry is conditioned with lime in order to raise the pH. The slurry is subjected to a copper flotation process, using a collector and frother as required. However, when copper rimmed pyrite is encountered, the process is unsatisfactory due to inefficiency in achieving the desired separation of chalcopyrite from pyrite. By way of example, a typical traditional process yields a copper concentrate which assays about 10 weight percent to about 17 weight percent copper after flotation, as opposed to a theoretical maximum of about 33 weight percent copper if the concentrate is 100 percent chalcopyrite. The main diluent is typically copper rimmed pyrite which floats with the chalcopyrite.
Practitioners of the froth flotation art have sought to separate chalcopyrite from rimmed pyrite, but have met with limited success. One method which has been employed to enhance the separation of chalcopyrite from copper rimmed pyrite is to grind the rimmed pyrite to an extremely fine size, e.g., less than 625 mesh. In this way, particles are formed which have little or no copper sulfide coating on their surfaces and the chalcopyrite is separated from these non-rimmed particles using conventional flotation techniques. However, it is relatively expensive to grind the minerals to such an extremely fine size, and the degree of separation may still be less than desired.
As a result, it would be advantageous to have a process for efficiently and economically separating chalcopyrite from copper rimmed iron sulfides. In particular, it would be advantageous to have a froth flotation process for effectively separating chalcopyrite from copper rimmed pyrite. It would be advantageous if the process for separating chalcopyrite from rimmed pyrite could be accomplished using ordinary froth flotation equipment and would result in a copper concentrate having a relatively high concentration of copper.